1. Field of the Invention
The invention relates generally to a detection cell for receiving a sample to be analyzed photometrically. More specifically, the invention is directed to a detection cell for receiving a sample to be analyzed photometrically that guides excitation light used to detect separated components or peaks through the detection cell, thereby reducing the signal variation of the excitation light and minimizing its potential to wander off axis.
2. Description of Related Art
In biotechnology, separation and analysis of biochemical samples is critically important. Moreover, it is desirable to conduct multiple separations and analyses of the separated components simultaneously to increase the speed and efficiency at which biological samples are evaluated. For example, separation technologies such as electrophoresis are used in DNA sequencing, protein molecular weight determination, genetic mapping, and other types of processes used to gather large amounts of analytical information about particular biological samples. More recently plastic microchips or lab-on-a chip technology is being used to perform separations of biological samples.
Capillary electrophoresis is a particularly preferred separation method. In this method, a sample is electrophoretically separated into its various components or peaks in a capillary tube filled with a buffer solution or gel. This technique allows the use of high electric fields, since the capillary tube efficiently dissipates the resulting heat produced by the electric field. As such, the separations achieved are much better than more traditional electrophoretic systems. In addition, multiple capillary tubes may be closely spaced together and used simultaneously to increase sample through-put.
Analysis or detection of the separated components can be performed while the sample is still located within the capillary and may be accomplished using photometric techniques such as adsorbance and fluorescence, wherein excitation light is directed toward the capillary tube, and light emitted from the sample (e.g., fluorescence) is measured by a detector, thereby providing information about the separated components. Other analytical techniques such as radioactivity detection, electrochemical methods, and mass spectrometry, may also be used to analysis the separated components. Typically, a photometric method such as laser-induced-fluorescence is used wherein the source of the excitation light is a laser that is directed towards the capillary, and the resulting fluorescence from the separated components is measured by a detector. However, the quality of this photometric scheme is reduced due to scattering (e.g., reflection or refraction) of the light by the capillary walls. In systems employing multiple capillary tubes, the laser beam may sequentially scan each capillary tube or may simultaneously traverse the entire plurality of tubes. In either case, light scattering remains a problem, particularly since reflected or refracted light from one capillary tube may interfere with the detection of fluorescence from an adjacent capillary tube or create a complete or significant loss of signal altogether.
As such, there is a need for an improved detection cell that provides better control over the direction within the detection cell of the excitation light that is used to analyze or detect separated components or peaks that have been produced using such techniques such as capillary electrophoresis or microchip technology. Further, there is a need for an improved method for utilizing a detection cell to provide such control over the direction of the excitation light within the detection cell.
The detection cell of the present invention provides a device for use in analyzing or detecting separated components or peaks from a capillary electrophoresis system, microchip system, or other analytical technique for separating a chemical or biological sample into components. Specifically, the detection cell of the present invention can be used in conjunction with laser-induced fluorescence detection techniques conducted outside of a capillary or microchip channel. The detection cell of the present invention can be used with or without sheath-flow technology and also in conjunction with electro-flow techniques, such as those described in U.S. Pat. No. 5,833,826, incorporated herein by reference.
Specifically, the detection cell of the present invention guides excitation light through the detection cell, which may contain a support matrix comprising a buffer solution or polymer solution, thereby reducing or eliminating the potential for the light to wander off axis. As a result, refraction of the excitation light is reduced or avoided, and thus a stronger signal may be emitted from the separated components making detection of that signal easier. In addition, the excitation light can be confined within the detection cell to that region in which the separated components are flowing, thereby reducing or avoiding a potential loss of signal that may otherwise result if the excitation light wandered off axis and did not illuminate a separated component. Additionally, the present invention provides for easier alignment of the excitation light with the detection cell Furthermore, where the detection cell is made from a low index of refraction material, the background fluorescence is reduced, thereby making detection easier and making the measurement of the resulting fluorescence more robust.
Accordingly, in one embodiment, the present invention provides a detection cell that comprises a body having a first end that defines a first opening, a second end that defines a second opening, and an internal surface that defines an interior cavity that fluidly connects the first opening and the second opening; wherein the interior cavity is capable of holding a support matrix for receiving a chemical species through the first opening, passing the chemical species through the interior cavity, and discharging the chemical species through the second opening; and wherein at least two portions of the body are capable of providing a first and a second guiding region each having an index of refraction less than that of the support matrix.
In another embodiment, the present invention provides a method for guiding light through a support matrix through which a chemical species is passing, comprising directing a beam of light toward a support matrix; and establishing a first and a second guiding region adjacent to and extending along at least a portion of the axis of travel of the beam of light within said support matrix, wherein the first and the second guiding regions each have an index of refraction that is less than that of the support matrix and wherein the first guiding region is approximately opposite the second guiding region, thereby maintaining the beam of light substantially between the first and the second guiding regions.
In yet another embodiment, the present invention provides a system for guiding light through a support matrix to detect a chemical species, comprising a detection cell comprising a body having a first end that defines a first opening, a second end that defines a second opening, and an internal surface that defines an interior cavity that fluidly connects the first opening and the second opening; a support matrix capable of receiving a chemical species through the first opening, passing the chemical species through the interior cavity, and discharging the chemical species through the second opening; wherein at least two portions of the body are capable of providing a first and a second guiding region each having an index of refraction less than that of the support matrix.
These and other features of the invention will appear from the following description from which the preferred embodiments are set forth in detail in conjunction with the accompanying drawings.